1. Field of the Invention
This invention relates to a novel die casting apparatus for producing firm products having a fine tissue while minimizing a creation of blowholes which has been a fatal disadvantage in the die casting method.
2. Description of the Prior Art
In order to prevent occurrence of blowholes, the interior of a mold is being subjected to secondary processing.
In this case, a secondary processing pressure naturally has to be transmitted into the product, i.e., portions where blowholes are created prior to solidification of molten metal within the mold. However, time at which molten metal is solidified and time required to solidify molten metal area varied according to materials, temperatures, wall thickness of products, etc.
It is desirable that starting time of the secondary processing, pressing time and pressing pressure may be adjusted.
However, in conventional methods, these points have not been taken into consideration, and in addition, a secondary pressing cylinder by electric signals wherein an injection cylinder is detected by a pressure switch, said signal being input into a timer, and as a result, a delay in pressing occurs failing to obtain an effective secondary pressing effect. In order to compensate for this, pressure more than as needed had to be often used for pressing.
Moreover, according to the signals obtained by said detection means, operating timing is unstable to make it difficult to stably recur a desired operation starting time, thus rendering the effect of the secondary pressing unsatisfactory.
Furthermore, a plurality of die casting machines having different performance are used in actual production site. When mold of the same design are applied to these machines which are different in performance from each other, uniform products may not be obtained.